Our starting point will be the model developed in [1]}, [2]}, [3]}, where the displacement minimizes an elastic energy that decomposes as:
\(\mathcal {E}[\mathbf {u}_1, \mathbf {u}_2] = \sum _{j=1}^2 \mathcal {E}^j_\mathrm {intra}(\mathbf {u}_j) + \mathcal {E}_\mathrm {inter}(\mathbf {u}_1 - \mathbf {u}_2),\) 
